An accurate estimate of the momentary air interface load of the uplink in a cellular system such as a WCDMA system is necessary in order to enable accurate scheduling of users of the uplink, exemplified by the enhanced uplink, EUL, in WCDMA and for the accurate admission of new users of the WCDMA uplink. Inaccuracies in the estimation of the momentary air interface load of the WCDMA uplink will result in a reduction of the throughput of the WCDMA EUL uplink.
The air interface load is expressed as a so called noise rise, i.e. the total amount of (relevant) interference power, divided by the thermal noise of the WCDMA uplink receiver. From this, it follows that in order to obtain an accurate estimation of the air interface load, it is also necessary to obtain an accurate estimation of the thermal “noise floor” in the receiver—due, for example, to the fact that variations in electronics components result in thermal noise floor variations of 1-3 dB between different uplink receivers, i.e. NodeBs with the continued use of a WCDMA system as an example, and also due to the fact that factory calibration would be costly as well as being uncertain due to highly varying installation procedures and corresponding variations in cabling losses.
Estimation of the thermal noise floor in the receiver in a WCDMA NodeB is a difficult problem, one of the sources of the difficulty being that it is not possible to distinguish between interference from neighboring cells and the receiver's internal noise, i.e. the receiver's thermal noise.
Interference from neighboring cells will thus often cause an estimation of the receiver's internal noise floor to be too high. In addition, the amount of interference from neighboring cells varies over time, a fact that sometimes allows for accurate noise floor estimation and sometimes not. A remedy for time-varying interference from neighbouring cells would of course be to extend the period of time over which the internal noise floor is estimated. However, this has two distinct drawbacks: first of all, the bandwidth of the noise floor estimator will be reduced, and secondly, the amount of data needed for the estimations is increased.
In addition, the “always connected” ambition of the cellular industry, together with the ambition to have a large number of users, e.g. smart phones and machines, which simultaneously use the uplink will make the problem of “seeing” the internal noise floor in a receiver in a NodeB much worse in the future, due to the fact that “always connected” devices will transmit with low intensity, and the large amounts of such users will greatly reduce the variation of the uplink load, simply due to “the law of large numbers”, thus making the interference level appear as slightly varying around a mean value that varies slowly.
There exist methods for estimating the internal noise floor in a receiver, but these known methods exhibit a number of disadvantages. Some known methods include so called bias estimation, and some don't. Known methods without bias estimation exhibits such disadvantages as providing estimates that are biased towards positive values and of providing estimates that vary substantially over time. Known methods with bias estimation exhibit disadvantages that include, for example, an inability to provide a sufficient amount of bias reduction, i.e. they are not accurate enough, in addition to which they do not provide bias estimations with a sufficiently high degree of resolution, e.g. by the hour per day, as well as being unable to provide bias estimations that perform differently for different weekdays, which would be necessary due to the fact that the uplink traffic intensity varies between, for example, weekdays and weekends. In addition, such known methods for estimating the internal noise floor in a receiver often rely on auxiliary measurements, which requires the development of auxiliary interfaces and signal transfer protocols.
In addition, as mentioned previously, known methods for estimating a receiver's internal noise floor are not able to cope with the “always connected” ambition of the cellular industry, in connection with the ambition to have large numbers of users, e.g. smart phones and machines, which simultaneously use the uplink.